1. Field of the Invention
The present invention relates to an object detection apparatus and an object detection method for detecting a target object in an image.
2. Description of the Prior Art
Conventionally, various methods have been proposed for detecting a target object in an image. For example, as a method for detecting a human head in an image, some methods are proposed as described in Japanese unexamined patent publications No. 2001-222719, No. 9-35069 and No. 2001-175868.
According to the method described in Japanese unexamined patent publication No. 2001-222719, a human head is regarded as an elliptical shape, and the human head (i.e., the elliptical shape) is detected in an image by a vote process that is one type of Hough transformation (hereinafter, it may be referred to as “Hough transformation method”) using an elliptical template.
According to the method described in Japanese unexamined patent publication No. 9-35069, a template that lay emphasis on a part of the elliptical shape is used for detecting the head (the elliptical shape) in an image. By using this template, the head (the elliptical shape) can be detected even if an occlusion is generated in a part of the head to be detected.
According to the method described in Japanese unexamined patent publication No. 2001-175868, directional properties of edges at plural points on the contour of the human body are calculated as characteristic quantities, and the human body is detected by evaluating the characteristic quantities in a comprehensive manner.
However, the method described in Japanese unexamined patent publication No. 2001-222719 has a disadvantage that if an occlusion is generated in a part of the head to be detected, the head may not be detected effectively. In other words, the accuracy of detection may be deteriorated in such a case.
The method described in Japanese unexamined patent publication No. 9-35069 can detect the head even if the above-mentioned occlusion is generated but has a disadvantage that the template is complicated so that the process requires much time.
The method described in Japanese unexamined patent publication No. 2001-175868 has a disadvantage that plural edges indicating different directional properties are necessary so that the process requires much time.